Manufacture of ductile bodies from highly-refractory metals



p 17, 1929- J. A. VAN LIEMPTV 1,728,814

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Patented Sept. 17, 1929 UNITED STATES PATENT OFFICE JOHANNES A. VAN LIEMPT, OI EINIDHOVEN, NETHERLANDS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK MANUFACTURE OF DUCTILE BODIES FROM HIGHLY-REFRACTORY METALS Application filed January 16, 1925, Serial No. 2,881, and in the Netherlands January 24,1924.

This invention relates to an improvement in, or modification of, the invention described in United States Letters Patent No. 1,601,931, issued July 22, 1924. i

For manufacturing helically wound filaments intended for electric incandescent lamps and consisting of a single crystal, filaments consisting of one crystal may be submitted to a helically winding operation. It has however, been found that in helical wires made in this manner, internal stresses may occur by reason of the helically winding operation and the said stresses, during the operation of the incandescent lamps in which, the helical wires have been disposed, may result in deformations ofthe incandescent helix, which exercise a very unfavourable influence on the incandescent lamp and may 'even render it useless;

In order-to obviate the said disadvantage it has been suggested to heat the filament to a high temperature subsequent to the helically winding operation. Thus the internal stresses generated in the filament by the helically winding operation are suppressed. Helical wires thus manufactured, do not yet satisfy lunverer, the conditions underlying filaments for electric incandescent lamps and furthermore it is not possible to obtain in this manner hclically wound filaments having a diameter that allows for their use in high current incandescent lamps such for example, as projection lamps.

The invention relates to the manufacture of ductile bodies from high refractory metals in accordance with the main Patent No. 1,601.931. The process according to the main specification consists in that a single metal crystal is heated in an atmosphere of a volatile and dissociable compound of the same metal to a ten'lperature at which the compound dissociates and at which the liberated metal deposits on the crystal such that the latter increases in size while keeping its onecrystal structure.

The dissociable compound of the refractory metal can be associated with small quancities of other substances which are adapted to form with the refractory metal a single crystal. The crystal to be treated can be placed in a continuous current of the vapor of the dissociable compound.

The cross-section of the crystal treated according to main application increases in a very regular manner, till only practical considerations make it necessary to stop. The body obtained is so ductile that it may be immediately shaped into any desired form by mechanical operations such as a hammering or rolling or drawing.

For manufacturing bodies of tungstenaccording to one embodiment of the invention disclosed in the main application a tungsten crystal is heated in an atmosphere of chloride of tungsten to a temperature between 1200 and 24-00" C. The metal dissociating from the chloride settles onthe tungsten crystal, so that the latter increases in cross-section while remaining only a single crystal. For

manufacturing wires, threads, ribbons or plates the original body is allowed to increase insize in the atmosphere of chloride to the extent desired. The body obtained in this way, may be given the desired shape by mechanical treatment. Thus wires for electric .lamps may be manufactured directly from such ductile material and. strong wires can be obtained after further mechanical treatment.

The original crystal in the main applica. tion instead of being a crystal of the same material as the final ductile body, may be a crystal of another metal or a metal alloy, provided the crystal form of this metal or alloy is isomorphous with that of the material of the ductile body. In this case the core may be removed in any known manner after the formation of the body.

It may be useful, in order to improve theproperties of the final productaccording to the main application to add to the atmosphere in which the refractory metal such as tungsten is treated, small quantities of substances such as iron, nickel, phosphorus, or silicon. The additional substances must be such as can form a single crystal with the refractory metal, without disturbing the uniform crystallization. The substances are added by incorporating them in a volatile state in the atmosphere in which the crystal -ample for use in carrying out the process according to the main application.

In this drawing, 1 is a vessel, for example of heat resisting glass, in which an atmosphere of chloride of tungsten is provided. This vessel is closed by two covers 2 which may be secured to or against the vessel in any suitable manner. Through each of the covers a tungsten rod is inserted and these. rods u port at their ends a single tungsten crystal 4. The vessel 1 is provided with a conduit 5 through which it can be exhausted. The vessel rests on supports 9 in a furnace 8. The interior of the furnace is maintained at such a temperature that the chloride of tungsten does not condense on the walls of the vessel 1.

The heating of the Vessel may be effected by a hot current of air, entering through a con-' dnit 11 and leaving through a conduit 12, but the furnace can be heated in any other suitable way.

A' cup 6 filled with tungsten powder is placed in the vessel. The tungsten powder may contain some additional substance as hereinbefore mentioned.

After the vessel is exhausted and filled with vapour of chloride of tungsten, the body 4 is heated to about 1500 to 1600 C. by an electric current, whilst the powder in the cup 6 is heated in some way to a temperature of 300-500 C. 'According to the drawing the powder is electrically heated bymeans of a resistance wire 7. The vapour then dissociates at the surface of the body 4 on which it deposits tungsten, while the liberated dissociation products combine with the powder in the cup 6 to form new compounds capable of dissociation.

The way of heating the body 4 and th powder may be varied according to circumstances. It is not necessary that the powder and the crystal should be enclosed in the same chamber but the vapour may be led from the powder-to the crystal in a circulating process. Instead of tungsten powder it is possible to use tungsten in any other form the temperature to which it is heated, being Varied accordingly while chloride of tungsten canbe replaced by other volatile tungsten compounds, which are capable of dissociation.

It is to be understood, that although the process is particularly described for manufacturing bodies of tungsten, the invention is also practicable for other refractory metals, such as molybdenum, tantalum and the like, which are able to form compounds that are dissociable at a. temperature below the melting point of the metal.

With the foregoing description of the process of the main specification, the present inreference to an example. A tungsten onecrystal wire having a diameter of 100 microns is initially helically wound in accordance with a known method. The size and the pitch of the turns are so chosen as to be suitable for a helical filament, having the desired diameter obtained by heating the dissociable compound.

The tungsten helix thus formed is introduced into an apparatus as described in the main specification and is heated in an atmosphere of tungsten.hexachloride to a temperature lying between 1200 and 24:00 in the same manner as indicated in the main'specification.

Helical filaments made in accordance with the invention are especially suitable for high current incandescent lamps, such as projection lamps. The drawing used in connection with this specification is of course more or less diagrammatic but in View of the description it is obvious that the apparatus may be varied by those skilled in the art more or less as their skill may suggest without departing from the. spirit of the invention or the scope of the claim. herein.

What I claim as new and desire to secure by Letters Patent of the United States, is:

The process of making a coiled unicrystalline filament from a highly refractory metal which comprises forming a unicrystalline wire into a coil and heating the coiled wire in an atmosphere of a volatile and dissociable compound of the same metal to a temperature at which said compound dissociates and the liberated metal deposits on said coiled wire whereby the diameter of the coiled wire is increased and any deleterious stresses in the wire, due to coiling, are removed.

In witness whereof, I have hereunto set my hand this th day of December, 1924.

J OHANNES A. VAN LIEMPT. 

